The proposed research is concerned with the age-related loss of proliferative and antibody forming ability of immunocytes and with the use of immunosuppressants in reversing cellular and whole animal senescence. The study involves the isolation and identification of 19S and 7S mouse spleen antibody forming cells through the use of the hemolytic-plaque technique. Isolated antibody forming cells are analyzed cytochemically. Experiments will be performed on young and on old mice. The immunosuppressants, hydrocortisone, antilymphocytic-serum, and azathioprine will be investigated for their roles in immunological rejuvenation.